1. Field of the Invention
The present invention relates to an optical head, a magneto-optical head, a disk apparatus, and a manufacturing method of the optical head, and in particular, relates to an optical head, a magneto-optical head, and a disk apparatus, that have high optical efficiency, can realize high-density recording media and perform high-speed recording and reproduction, and can prevent erroneous reproduction, and a manufacturing method of the optical head.
2. Related Art
Recently, to improve the recording density of a magneto-optical disk or a magnetic disk, which records data with light and a magnetic field, or an optical disk, which records data only with light, reducing a spot size of the near field light used for record or reproduction has been investigated.
As conventional disk apparatuses using this miniaturized near field light, there are what are shown in, for example, Japanese Patent Laid Open No. Hai 11-250460 (1999).
FIG. 16 shows the disk apparatus. This disk apparatus 80 has clear lens-like holding member 81 that is a transparent condensing medium, a laser source 83 emitting a laser beam 83a at an oblique angle to an incident surface 81a of the holding member 81, a scattering member 82 that is provided on a bottom surface 81b of the holding member 81 and has the size that is equal to or smaller than a wavelength of the beam, and a photo detector 89 detecting reflected light 87 from an optical disk 85 through an objective lens 88. In the disk 80 configured in this manner, the laser beam 83a from the laser source 83 is made to enter the incident surface 81a at an oblique angle so as to be totally reflected at the bottom surface 81b of the holding member 81 to be condensed and applied at a position of the scattering member 82. The plasmon resonance is generated in the scattering member 82, and a scattered light (near field light) 84 generated therefrom enters to a recording film 86 of the optical disk 85. Then, reflected light 87 from the recording film 86 is guided to the photo detector 89 by the objective lens 88 and detected by the photo detector 89. Since it is possible to obtain the near field light 84 with the minute size that is a fraction of one or less of the size in a case of only the holding member 81, it is possible to increase recording density.
According to a conventional disk apparatus, since the laser beam 83a enters the holding member 81 at an oblique angle, the irradiated area with the laser beam 83a at the incident surface 81a of the holding member 81, and so the numerical aperture of the incident laser beam becomes small. Hence optical efficiency becomes low. This causes a problem that a high-power light source becomes necessary, and a photo detector for reproduction becomes large.
On the other hand, if a laser beam is applied right above the holding member 81, the surface 81a of the holding member 81 becomes wide. Although optical efficiency is increased in this case, there is a probability of erroneously reproducing another recording area caused by the propagation light leaking out from a light spot position of the light-condensed surface 81b. 
FIG. 17 shows a metal structure described in the Dig. of the 6th Int. Conf. on Near-Field Optics and Related Tech. 2000, No. MoO13 (2000). As shown in FIG. 22, the metal structure consists of small metal bodies 91a and 91axe2x80x2 faced each other with a small gap 9 between them. The width of apexes 91b and 91bxe2x80x2 of the metal bodies and the gap 91c are about 20 nm and far less than the wavelength of incident laser beam 92.
By arranging the polarization direction of the incident laser beam 92 to cross over the gap, a surface plasmon is excited in the metal bodies 92a and 92axe2x80x2 and vibrated in the direction parallel to the polarization direction, and electric charges having opposite polarities with each other in the apexes 92b and 92bxe2x80x2 causes dipole and the dipole generates the plasmon effectively. The induced electric charges which constitute an electric dipole, generate a strong near-field light 93 effectively, the size of which is nearly equal to that of the gap 92c. 
The simulation rest shows that the dipole excited emit a near-field list which intensity is 2300 times larger than that of the incident light and is emitted only around the gap 91c. An experimental result about micro wave radiation with a dipole antenna (R. D. Grober et al.: Appl. Phys. Lett., Vol. 70, No. 11, (1997) p. 1354) shows that the radiation occurs only around the gap region. The reason is that the antenna acts as a shield for the incident microwave because the conductivity of the metal antenna is so high enough to induce a strong dipole and the dipole has a strong shield effect.
In the case of the visible frequency region, the most of the incident wave passes side of the metal shade without coupling to the metal shade and is emitted out from the bottom surface of the transparent condensing medium, because the conductivity of the meal shade is not high enough to shield the incident wave, and the spot size of the incident is fairly larger than the size of the metal and its gap. Further to incident beam of the prior art bodies vertically, so the component of the propagation light of the light leaking out from a light spot is much more than the component of the near field light. The propagation light becomes the background noise of the optical recording and reproducing the near field light. In FIG. 17, The poised beam 92b, i.e. propagation light, irradiates and affects a recording medium when the medium is placed just under the metal bodies 92a and 92a for applying the near-field light for recording, which prevents the near-field light to make recorded marks even if the size of the near-field light could be small enough.
The present invention has been made in view of the above circumstances and provides an optical head, a magneto optical head, and a disk apparatus that have high optical efficiency, and can realize high-density recording media and perform high-speed recording and reproduction, and a manufacturing method of the optical head.
In addition, the present invention also provides an optical head, a magneto-optical head, and a disk apparatus and a manufacturing method of the optical head that can prevent erroneous reproduction.
According to a first aspect of the present invention, an optical head includes: a laser emits a laser beam; an optical system that has a transparent condensing medium which condenses the laser beam from the laser source and forms a light spot on a light-condensed surface of the transparent condensing medium; a shade provided in an optical path of the laser beam from the laser to the transparent condensing medium and shields a central part of the laser beam and a micro metal member provided so that at least part of the micro metal member is in a position where the light spot is formed and the size of the part of the metal member is smaller than that of the light spot.
According to the above configuration, the laser beam emitted from the laser source enters the transparent condensing medium with its central part being shielded by the shade, and forms the light spot on the light-condensed surface. Since the central part of the laser beam emitted from the laser source is shielded, the propagation light can be prevented from leaking out from the light-condensed surface. When the laser beam is irradiated to the micro metal member provided at a position of the light spot being formed, the plasmon is excited in the micro metal member is excited and near field light having one-digit or higher of multiplication of intensity in comparison with an incident beam is generated. By irradiating a recording medium with this near field light, recording and reproduction becomes possible. Since the size of the near field light is almost the same as the size of the micro metal member, by reducing the size of the micro metal member to reduce the size of the near field light, high-density recording becomes possible.
According to another aspect of the present invention, an optical head includes: a laser emitting a laser beam whose light intensity in a central part is lower than that in a periphery; an optical system that has a transparent condensing medium which condenses the laser beam from the laser source and forms a light spot on a light-condensed surface of transparent condensing medium; and a micro metal provided so that at least a part of micro metal member is in a position where the light spot is formed and the size of the part of the micro metal member is smaller than that of the light spot.
According to another aspect of the present invention, an optical head include: a laser emitting a laser beam; an optical system that has a transparent condensing medium which has a incident surface and a light-condensed surface and condenses the laser beam from the laser and forms a light spot on the light-condensed surface of the transparent condensing medium; and a micro metal member that is provided so that at least a part of the micro metal member is in a position where the light spot is formed and the size of the part of the micro metal member is smaller than the size of the light spot. The optical system has a numerical aperture of 0.8 or more of the laser beam entering the incident surface.
Another aspect of the present invention provides a magneto-optical head including: a laser emitting a laser beam; an optical system that has a transparent condensing medium which condenses the laser beam from the laser source and forms a light spot on a light-condensed surface of the transparent condensing medium; a shade provided in an optical path of the laser beam from the laser to the transparent condensing medium and shields a central part of the laser beam; a micro metal member provided so that at least a part of the micro metal member is in a position where the light spot is formed and the size of the part of the micro metal member is smaller than that of the light spot, an electromagnet that is provided near the micro metal member and generates a modulated magnetic field according to recorded information; and a magnetic resistive sensor detecting the recorded information as magnetic information.
According to another aspect of the present invention, a disk apparatus includes: a disk on which a recording medium is formed a laser emitting a laser beam; an optical system that has a transparent condensing medium which condenses the laser beam from the laser and forms a light spot on a light-condensed surface of the transparent condensing medium; a shade provided in an optical path of the laser beam leading from the laser to the transparent condensing medium and shields a central part of the laser beam; a micro metal member provided so that at least part of the micro metal member is in a position when the light spot is formed and the size of the part of the micro metal member is smaller than that of the light spot; and a moving mechanism relatively moving light outgoing from the micro metal member to the recording medium.
According to another aspect of the present invention a disk apparatus includes: a disk on which a recording medium is formed; a laser emitting a laser beam; an optical system that has a transparent condensing medium which condenses the laser beam from the laser and forms a light spot on a light-condensed surface of the transparent condensing medium; a first shade provided in an optical path of the laser beam from the laser to the transparent condensing medium and shields a central part of the laser beam; a micro metal member provided so that at least part of the micro metal member is in a position where the light spot is formed and the size of the part of the micro metal member is smaller than that of the light spot; a moving mechanism relatively moving light emitted from the micro metal member to the recording medium; a detector detecting reflected light, based on a laser beam emitted from the laser to the recording medium through the optical system, through the transparent condensing medium; and a second shade shielding returned light lest the returned light that is part of the laser beam condensed on the light-condensed surface of the transparent condensing medium and is reflected on the light-condensed surface should enter the detector.
According to another aspect of the present invention, a manufacturing method of an optical head includes the steps of: preparing a transparent condensing medium having a light-condensed surface where a light spot is formed by an incident laser beam; covering an area except an area having the size smaller than the size of light spot on the light-condensed surface of the transparent condensing medium with photoresist; forming a concave part in the light-condensed surface by removing an area, where the photoresist is not present, in predetermined depth, which is equal to or shallower than a wavelength of the laser beam, by etching; and forming a micro metal member by depositing metal material in the concave part.
According to another aspect of the present invention a manufacturing method of an optical head includes the steps of: preparing a transparent condensing medium having a light-condensed surface where a light spot is formed by an incident laser beam; and forming a micro metal member, having the size smaller than the size of the light spot, by depositing a metal film in a central part of the light spot on the light-condensed surface of the transparent condensing medium by a focused ion beam method.